This invention relates to antennas and, more particularly to loop antennas having an input impedance which is low relative to prior antennas of this type.
Loop antennas of the general type illustrated in FIG. 4 are well known. For example, a square loop that is 0.5 meters on each side, formed of a conductor of one inch diameter, will have a reactance of about 37 Ohms at a frequency of 5 MHz.
U.S. Pat. No. 5,402,133 issued to J. T. Merenda on Mar. 28, 1995, ("Merenda") describes synthesizer radiating systems capable of providing efficient wideband operation with use of a small loop antenna. The word "small" being used to refer to antenna size relative to wavelength. The disclosure of the Merenda patent is hereby incorporated by reference herein.
In application of antenna systems in accordance with the Merenda patent it is desirable to provide low impedance loop antennas. In particular applications, the 37.3 ohm impedance of the loop antenna referred to above is higher, by a factor of about four, than the impedance level required in order to approach optimal performance in a Merenda antenna system implemented with available circuit devices separate from the antenna.
For use in Merenda antenna systems and other applications for very low impedance antennas it is, therefore, desirable to provide new forms of loop antennas characterized by low impedance without significant degradation of the radiation Q of the antenna system.
Objects of the present invention are to provide new and improved types of loop antennas and such antennas having one or more of the following advantages and characteristics:
low input impedance, relative to prior loop antennas; PA1 limited Q degradation, relative to prior loop antennas; PA1 small size, relative to operating frequency; PA1 wideband operation; PA1 incorporated feed network; PA1 readily accommodated coaxial connector feed; PA1 flexible, sheet construction; PA1 economical fabrication; and PA1 sturdy, high-reliability construction.